Project Spotlight: Mule Deer Diet in the Texas Panhandle
In the Texas Panhandle, it is not uncommon to see 50 to 100 mule deer at a time on a wheat field during winter. While most landowners enjoy seeing these deer, concerns about crop damage have increased, raising many questions about the relationship between mule deer and agriculture.
Beginning in autumn of 2015, researchers from Texas Parks and Wildlife Department, Borderlands Research Institute at Sul Ross State University, Caesar Kleberg Wildlife Research Institute at Texas A&M University-Kingsville, and Texas Tech University came together to better understand how agriculture influences mule deer in the Texas Panhandle. The collaborative study is looking at various aspects of mule deer ecology: movement, survival, antler size, body condition, fawn recruitment, diet, and nutrition. With the Borderlands Research Institute, graduate student Jacob Lampman is focusing on the latter of these—how agriculture influences mule deer diets and nutrition.
For this study, from 2015–2017, mule deer were captured and studied near Turkey, Texas—an area intermixed with both native rangeland and agriculture (predominantly wheat and cotton fields).
The first objective was to determine what mule deer were eating throughout the year. To collect the needed information, mule deer were closely observed during the day, and fecal samples were collected and analyzed using a relatively new technique called DNA metabarcoding. On a fundamental level, this technique identifies what plants the deer has eaten based on the plant DNA found in the fecal samples. By analyzing every sample collected, we can get an idea of what plants and crops deer are eating throughout the year and compare diets among seasons.
We found that mule deer diets within the study area largely consisted of forbs and browse throughout most of the year—species like Missouri primrose, western ragweed, shinnery and Mohr oak, redroot pigweed, and prairie fleabane. Wheat and cotton were the most common crops in the study area and were eaten during their growing seasons, with a preference shown for wheat.
To complement the diet analyses, samples of forage and crop species were collected to estimate nutritional forage value. Samples were composed only of the portions of the plants that are readily consumed by mule deer (new growth stems, green leaves, flowers, and fruit). This method mimics how deer select different parts of plants and gives an accurate estimate of the nutritional value of the foods the deer may eat. The plant samples were then taken back to a lab at Sul Ross State University where digestible energy and protein were estimated in each plant every month.
Last, we looked at what factors in nutritional value drove mule deer to select forage species. Farmers and ranchers notice that mule deer gather on wheat fields during the winter and then disperse in the spring, and diet and GPS location data confirm these movements. As the wheat matures and diminishes in nutritive quality, and as rainfall causes new growth of high-quality rangeland plants, a seasonal shift back to rangeland forage occurs. Mule deer are taking advantage of winter wheat during late fall and winter for both energy and protein reasons. Energy is needed during this time for fat accumulation and rut activities, but an easily accessible and digested forage that provides high protein content is vastly superior to rangeland plants during this time. In conclusion, winter wheat acts as a key supplemental forage during winter when forage diversity and nutrition is low.
Nutritional ecology is a foundational building block in understanding mule deer populations. By accruing knowledge about how mule deer fulfill their nutritional needs we begin to understand how the habitat influences other characteristics of their lives, including movement, survival, fawn recruitment, and antler size. Along with the work of other project collaborators, we are beginning to piece the puzzle together in understanding the relationship between mule deer and agriculture in the Texas Panhandle.